Ultrasonic gas leak detectors measure the sound pressure waves generated by the turbulent flow when gas escapes from higher pressures to the ambient atmosphere. Such gas leak detectors are used as industrial safety devices to monitor the unwanted or unexpected release of combustible or toxic gases into the atmosphere. The leaks need to be identified quickly before they grow further in magnitude, to allow for timely remedial action to be taken. A drawback of conventional ultrasonic gas leak detectors that depend on thresholds and time delays for their functionality is the inability to effectively verify their performance in the field, and to conduct functional safety checks at proof test intervals. Proof testing is a requirement of safety instrumented systems to demonstrate that everything is working and performing as expected. Conventional ultrasonic gas leak detectors are unable to differentiate between the sound emitted by a real gas release and a remote ultrasonic test source to be used for periodic system performance check. This is a major inconvenience to the industrial facility that leads to either the bypassing of critical proof testing or a significant operating cost burden. Conventional ultrasonic gas leak detectors provide maintenance personnel with no means to functionally remote test the gas leak detector without the disruption caused by the need to disable alarms.